In a large mixing bowl, mix together the ground beef, pork sausage, breadcrumbs, parmesan cheese, eggs, Italian seasoning, and garlic powder until well combined. While you can mix it well with a mixing spoon, I find it easiest to use clean hands to mix it together.
Divide the meat mixture into 12 even-sized portions, shaping them into large balls.
Use the sauté feature of your Instant Pot and add the cooking oil. Once the oil is hot, add the meatballs and sear on each side for 1-2 minutes or until browned. Depending on the size of your Instant Pot you may need to sear the meatballs in batches so as to not overcrowd the pan.
Once the meatballs are seared, but not fully cooked through, cancel the sauté function and stir in the marinara sauce. Be sure to stir well and scrap up anything on the bottom of the pan.
Seal the Instant Pot and set it to pressure cook for 7 minutes.
Once the Instant Pot finishes cooking, allow it to naturally release for 5 minutes and then release any remaining steam.
Serve the meatballs and sauce hot over pasta, optional, and garnish with fresh, minced parsley, optional.